Surface modification method for fluoride luminescent material and fluoride luminescent material prepared therefrom

ABSTRACT

In a surface modification method for fluoride luminescent materials, an inorganic coating layer AxMFy coated substrate AxMFy:Mn4+ is mixed with an organic solution containing a metal phosphate, an alkoxysilane, an organic carboxylic acid or an organic amine. The solution is evaporated to give the organic-inorganic coating layer coated surface-modified fluoride luminescent material. The phosphor photoluminescence intensity and quantum efficiency of the modified phosphors can be maintained at 85%-95% under high temperature and high humidity conditions. After being coated with the inorganic coating layer, the surface defects of the phosphor are reduced, and the photoluminescence intensity and quantum yield of the phosphor are increased by 5%-15%. After being coated with the organic coating layer, the photoluminescence intensity of the phosphor is reduced &lt;3%.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. national entry of PCT internationalapplication serial number No. PCT/CN2019/111737, filed Oct. 17, 2019,which claims the priority of Chinese patent application 2018113489870filed on Nov. 13, 2018 with China National Intellectual PropertyAdministration, titled “SURFACE MODIFICATION METHOD FOR FLUORIDELUMINESCENT MATERIAL AND FLUORIDE LUMINESCENT MATERIAL PREPAREDTHEREFROM”, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to the technical field of rare earthluminescent material and illumination display, in particular to asurface modification method for fluoride luminescent materials and afluoride luminescent material prepared therefrom.

BACKGROUND

As a new type of solid-state light source, white LED has advantages suchas environmental protection, energy saving, high efficiency, and fastresponse compared with traditional light sources such as incandescentlamps and fluorescent lamps. It is honored as the fourth generation ofgreen light source following incandescent lamps, fluorescent lamps andhigh-pressure gas discharge lamps. In the LED light source, theperformance of phosphor determines the LED luminous efficiency, colorrendering index, color temperature and service life and other technicalindicators. Therefore, the phosphor plays an important role in white LEDand is widely concerned. At present, the most commonly used method is tocombine a blue LED chip (emitting wavelength at 440-480 nm) with ayellow phosphor (such as YAG:Ce or TAG:Ce). After the combination, theyellow phosphor absorbs the blue light from the blue LED chip to emit ayellow light, which mixes with an unabsorbed blue light to form a whitelight. However, in this way, only a cold white light device with acorrelated color temperature (CCT) greater than 4500 K and a lower colorrendering index less than 80 can be obtained. The main reason lies inthe lack of red light in the emission spectrum of commonly used yellowphosphors, which makes it difficult to obtain a white LED device withlow color temperature and high color rendering index, the keys to theindoor application of the white LED. In order to achieve this goal, aneffective way is to add an appropriate amount of red phosphors to awhite LED device to enhance the red emission of the device.

Mn⁴⁺-activated fluoride phosphors have a narrow emission peak with asmall half-peak width, and are the hotspots in the research of redlight-emitting materials. The patent application US2009/7497973disclosed a Mn⁴⁺-activated A₂MF₆ (A is K, Na, Rb, etc.; M is Ti, Si, Sn,Ge, etc.) red phosphor, which is obtained by dissolving the startingmaterial in hydrofluoric acid at a high concentration and then heatingthe volatile cocrystal. The patent application WO2009/119486 disclosed afluoride product, which is obtained by dissolving elemental Si in asolution of hydrofluoric acid and potassium permanganate. The patentapplication CN102732249A disclosed a fluoride product, which is obtainedby mixing the first solution containing the fluoride of metal M with thesecond solution containing A or the compound of A in a solid form, andreating to give the precipitate. The fluoride luminescent materialsprepared by those methods have the advantages of high photoluminescenceefficiency and good thermal stability. However, none of those methodshave overcome the shortcoming of easy hydrolysis of fluoride luminescentmaterials. Therefore, the fluoride luminescent materials are easy to behydrolyzed in long-term use or under a humid condition, leading to thedecrease of photoluminescence efficiency or even failure. The patentapplication US2007/0125984A1 reported a method for improving thehumidity resistance of a phosphor by coating a layer of inorganicmaterial (such as TiO₂, Al₂O₃, and SiO₂) on the surface of the phosphoras a protective film. However, such an aqueous phase coating techniqueis difficult to apply to the coating of fluoride phosphors. Similarly,the patent application CN106479485A disclosed a method for improving thehigh temperature and high humidity resistance of a phosphor by coating alayer of potassium silicate-sodium hydroxymethylcellulose-polyethyleneglycol mixture on the surface of the phosphor. However, such an organiccoating material has the disadvantages of high temperature intoleranceand easy decomposition, which affects the efficiency of long-term use ofphosphors. Therefore, it is of great practical significance to improvethe humidity resistance of fluoride phosphors while prolonging theservice life of white LED, which meets the requirements of energy savingand environmental protection.

SUMMARY

Mn⁴⁺-doped fluoride red phosphor is easy to hydrolyze under a humidcondition due to its poor humidity resistance, which leads to thedecrease of efficiency or even failure of the red phosphor and thereduction of the service life of LED. In order to improve the humidityresistance of the fluoride red phosphor, it is necessary to perform thesurface modification for phosphor material by coating an inorganic thinlayer or an organic thin layer on the surface of phosphor material toform a protective layer with humidity resistance.

In order to overcome the shortcomings of the prior art, the presentinvention is intended to provide a surface modification method forfluoride luminescent materials and a fluoride luminescent materialprepared therefrom. In the present invention, Mn⁴⁺ on the surface of asubstrate A_(x)MF_(y):Mn⁴⁺ is removed by ion exchange to form astructure of an inorganic coating layer A_(x)MF_(y) coated substrateA_(x)MF_(y):Mn⁴⁺, which is denoted as A_(x)MF_(y):Mn⁴⁺@A_(x)MF_(y). TheA_(x)MF_(y):Mn⁴⁺@A_(x)MF_(y) can effectively prevent the luminescencecenter inside the substrate A_(x)MF_(y):Mn⁴⁺ from transferring energy tothe surface to avoid the resulting fluorescence quenching and improvethe photoluminescence efficiency of the fluoride luminescent material.Then an organic coating layer is coated on the outer surface of theinorganic coating layer to form a hydrophobic layer, so as toeffectively improve the stability of fluoride luminescent materialsunder high temperature and high humidity conditions withoutsignificantly reducing the photoluminescence efficiency of fluorideluminescent materials. The method features simple preparation process,wide source of starting materials and low consumption of hydrofluoricacid, which is suitable for large-scale industrial preparation.

The purpose of the present invention can be achieved through thefollowing technical solutions:

A surface-modified fluoride luminescent material comprising a substrate,an inorganic coating layer and an organic coating layer, the inorganiccoating layer being coated on the outer surface of the substrate, andthe organic coating layer being coated on the outer surface of theinorganic coating layer; wherein

the substrate is A_(x)MF_(y):Mn⁴⁺, and the inorganic coating layer isA_(x)MF_(y); wherein A is selected from one of alkali metals Li, Na, K,Rb and Cs, and a combination thereof; M is selected from one of Ti, Si,Ge, Sn, Zr, Al, Bi, Ga and In, and a combination thereof; x is anabsolute value of the charge of [MF_(y)] ion; y is 4, 5, 6 or 7; andMn⁴⁺ is a luminescence center ion.

According to an embodiment of the present invention, preferably, x is anabsolute value of the charge of [MF₆] ion, and y is 6.

According to an embodiment of the present invention, preferably, theinorganic coating layer A_(x)MF_(y) is obtained by removing Mn⁴⁺ on thesurface layer of the substrate A_(x)MF_(y):Mn⁴⁺ by ion exchange.

According to an embodiment of the present invention, in thesurface-modified fluoride luminescent material, the inorganic coatinglayer can be a single layer or multiple layers, and the organic coatinglayer coated on the outer surface of the inorganic coating layer canalso be a single layer or multiple layers. As an example, a double-layercoating structure is that a single inorganic coating layer is coated onthe surface of a substrate, and an organic coating layer is coated onthe outer surface of the single inorganic coating layer. A multi-layercoating structure can be that multiple inorganic coating layers arecoated on the surface of a substrate, and a single organic coating layeris coated on the outer surface of the multiple inorganic layers; or thata single inorganic coating layer is coated on the surface of asubstrate, and multiple organic coating layers are coated on the outersurface of the single inorganic coating layer; or that multipleinorganic coating layers are coated on the surface of a substrate, andmultiple organic coatings are coated on the outer surface of themultiple inorganic coating layers.

The multiple organic coating layers are the same or different incomposition, and preferably, the adjacent organic coating layers aredifferent in composition.

According to an embodiment of the present invention, the inorganiccoating layer and the organic coating layer are bonded by a chemicalbond.

According to an embodiment of the present invention, the organic coatinglayer is at least one of metal phosphates, alkoxysilanes, organiccarboxylic acids and organic amines.

According to an embodiment of the present invention, the phosphate inthe metal phosphate is phosphomonoester or phosphodiester, for example,P(O)(OH)₂(OR) or P(O)(OH)(OR)₂, wherein R is hydrocarbyl, for example,alkyl (such as a C₁₋₂₀ alkyl).

According to an embodiment of the present invention, the phosphate isobtained by esterifying a phosphorus source with an alcohol, wherein thephosphorus source is selected from one of P₂O₅ and POCl₃, and acombination thereof, and the alcohol is at least one selected frommethanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol.

According to an embodiment of the present invention, the metal in themetal phosphate is a metal cation; for example, the metal in the metalphosphate is selected from one of Al, Ti, Si, Ga and Zn ions, and acombination thereof.

According to an embodiment of the present invention, the alkoxysilane isSi(OR¹)₃(R²), wherein R¹ is C₁₋₆ alkyl, and R² is C₁₋₂₀ alkyl or C₁₋₂₀alkenyl; for example, the alkoxysilane is selected from methyltrimethoxysilane, ethyl trimethoxysilane, n-propyl trimethoxysilane,n-octyl trimethoxysilane, ethenyl trimethoxysilane, dodecyltrimethoxysilane, hexadecyl trimethoxysilane, and octadecyltrimethoxysilane.

According to an embodiment of the present invention, the organiccarboxylic acid is R³COOH, wherein R³ is C₁₋₃₀ alkyl; for example, theorganic carboxylic acid is selected from oleic acid, stearic acid,docosanoic acid, octacosanoic acid, and lauric acid.

According to an embodiment of the present invention, the organic amineis NR⁴(R⁵)₂, wherein R⁴ is C₁₋₁₀ alkyl, and R⁵, which may be the same ordifferent, is H or C₁₋₁₀ alkyl; for example, the organic amine isselected from methylamine, ethylamine, propylamine, butylamine,octylamine, and hexylamine, and the corresponding secondary amine ortertiary amine. The corresponding one is the secondary amine or tertiaryamine of methylamine, ethylamine, propylamine, butylamine, octylamine,and hexylamine.

The present invention also provides a preparation method for thesurface-modified fluoride luminescent material, comprising the followingsteps:

(1) dissolving the compound A_(x)MF_(y) in hydrofluoric acid solution toform a saturated solution;(2) adding the substrate A_(x)MF_(y):Mn⁴⁺ into the saturated solution instep (1), and obtaining an inorganic coating layer A_(x)MF_(y) coatedsubstrate A_(x)MF_(y):Mn⁴⁺ by ion exchange reaction, which is denoted asA_(x)MF_(y):Mn⁴⁺@A_(x)MF_(y);(3) preparing an organic solution;(4) mixing the inorganic coating layer A_(x)MF_(y) coated substrateA_(x)MF_(y):Mn⁴⁺ in step (2) with the organic solution in step (3), andheating and stirring the mixture until the organic solvent is removed,to give the surface-modified fluoride luminescent material, which isdenoted as A_(x)MF_(y):Mn⁴⁺@A_(x)MF_(y)@organic layer;wherein A is selected from one of alkali metals Li, Na, K, Rb and Cs,and a combination thereof; M is selected from one of Ti, Si, Ge, Sn, Zr,Al, Bi, Ga and In, and a combination thereof; x is an absolute value ofthe charge of [MF_(y)] ion; y is 4, 5, 6 or 7; and Mn⁴⁺ is aluminescence center ion.

According to an embodiment of the present invention, in step (1), themass percentage of hydrofluoric acid in the hydrofluoric acid solutionis 20%-50%.

According to an embodiment of the present invention, in step (1), thesaturated solution is preferably formed at 20-90° C.

According to an embodiment of the present invention, in step (2), themass ratio of the substrate A_(x)MF_(y):Mn⁴⁺ to the compound A_(x)MF_(y)in the saturated solution in step (1) is 10:1-1:5, and preferably, 1:1.

According to an embodiment of the present invention, in step (2), theion exchange process is performed at 0-100° C., and preferably, at25-80° C.

According to an embodiment of the present invention, in step (2), theion exchange is performed for at least 30 s, for example, for at least 1min, and preferably, for at least 5 min.

According to an embodiment of the present invention, in step (2), theion exchange is performed under a continuous stirring condition.

According to an embodiment of the present invention, step (2) furthercomprises the following step: filtering and drying the mixture after theion exchange is completed.

According to an embodiment of the present invention, in step (3), theorganic solution is at least one of metal phosphate solution,alkoxysilane solution, organic carboxylic acid solution and organicamine solution, and the preparation process for the solution is, forexample:

dissolving an alkoxysilane, an organic carboxylic acid or an organicamine in an organic solvent, wherein the organic solvent is at least oneof methanol, ethanol, propanol, n-hexane, and cyclohexane; ormixing a metal source and a phosphorus source with an alcohol for areaction to give a metal phosphate solution, wherein the phosphorussource is selected from one of P₂O₅ and POCl₃, and a combinationthereof; the alcohol is at least one of methanol, ethanol, n-propanol,isopropanol, n-butanol, and isobutanol; and the metal source is metalnitrate, metal sulfate or metal oxalate, or one or more of metal organicsalts such as isopropoxide, ethoxide, propoxide or butoxide.

According to an embodiment of the present invention, in step (3), thecontent of the alkoxysilane, the organic carboxylic acid or the organicamine in the organic solvent is at least 1 wt. %, and preferably, 5 wt.%.

According to the embodiment of the present invention, preferably, themetal source is Al(NO₃)₃.9H₂O, Zn(NO₃)₂.6H₂O, titanium butoxide, oraluminum isopropoxide.

According to an embodiment of the present invention, in the organicsolution containing the metal phosphate, the mass percentage of themetal source is at least 0.1%, and the mass percentage of the phosphorussource is at least 10%.

According to an embodiment of the present invention, in step (4), thetemperature of the heating and stirring is at least 30° C., andpreferably, at least 50° C.

According to an embodiment of the present invention, in step (4), themass ratio of the inorganic coating layer A_(x)MF_(y) coated substrateA_(x)MF_(y):Mn⁴⁺ to the organic solution is 5:1-1:20, and preferably,1:1-1:5.

According to an embodiment of the present invention, step (4) furthercomprises the following step: washing with an alcohol solution oracetone, and drying.

According to an embodiment of the present invention, in step (2),preferably, the A_(x)MF_(y):Mn⁴⁺ is selected from A₂MF₆:Mn⁴⁺ andA₃MF₆:Mn⁴⁺, wherein the A₂MF₆:Mn⁴⁺ is selected from K₂TiF₆:Mn⁴⁺,K₂SiF₆:Mn⁴⁺, Na₂SiF₆:Mn⁴⁺, Na₂TiF₆:Mn⁴⁺, K₂GeF₆:Mn⁴⁺, Na₂SnF₆:Mn⁴⁺,Cs₂TiF₆:Mn⁴⁺ and Cs₂SiF₆:Mn⁴⁺, and preferably, the A₂MF₆:Mn⁴⁺ isselected from K₂TiF₆:Mn⁴⁺, K₂SiF₆:Mn⁴⁺ and K₂GeF₆:Mn⁴⁺.

Preferably, the A₃MF₆:Mn⁴⁺ is selected from Na₃AlF₆:Mn⁴⁺, K₃AlF₆:Mn⁴⁺,Li₃AlF₆:Mn⁴⁺, Rb₃AlF₆:Mn⁴⁺, Cs₃AlF₆:Mn⁴⁺, K₂NaAlF₆:Mn⁴⁺ andK₂LiAlF₆:Mn⁴⁺, and more preferably, the A₃MF₆:Mn⁴⁺ is selected fromNa₃AlF₆:Mn⁴⁺, K₃AlF₆:Mn⁴⁺ and K₂NaAlF₆:Mn⁴⁺.

According to an embodiment of the present invention, in step (1),preferably, the A_(x)MF_(y) is selected from A₂MF₆ and A₃MF₆, whereinthe A₂MF₆ is selected from K₂TiF₆, K₂SiF₆, Na₂SiF₆, Na₂TiF₆, K₂GeF₆,Na₂SnF₆, Cs₂TiF₆ and Cs₂SiF₆, and more preferably, the A₂MF₆ is selectedfrom K₂TiF₆, K₂SiF₆ and K₂GeF₆.

Preferably, the A₃MF₆ is selected from Na₃AlF₆, K₃AlF₆, Li₃AlF₆,Rb₃AlF₆, Cs₃AlF₆, K₂NaAlF₆ and K₂LiAlF₆, and more preferably, the A₃MF₆is selected from Na₃AlF₆, K₃AlF₆ and K₂NaAlF₆.

According to an embodiment of the present invention, in steps (2) and(4), the filtered product can be further washed with an organic solventsuch as absolute ethanol or acetone to remove the residual acid on thesurface, and dried.

In the present invention, when mixing a substrate A_(x)MF_(y):Mn⁴⁺ witha saturated solution of a compound A_(x)MF_(y) in hydrofluoric acid, theMn⁴⁺ on the surface layer of the substrate A_(x)MF_(y):Mn⁴⁺ is reactedwith the metal cation M in the saturated hydrofluoric acid solution ofthe compound A_(x)MF_(y) for ion exchange, so that surface layer of thesubstrate A_(x)MF_(y):Mn⁴⁺ is free of Me, and a core-shell structure ofthe inorganic coating layer A_(x)MF_(y) coated substrateA_(x)MF_(y):Mn⁴⁺ is formed, with the particle size of the substrateA_(x)MF_(y):Mn⁴⁺ not changed. The prepared intermediate can effectivelyprevent the internal luminescence center of the phosphor fromtransferring energy to the quenching center on the surface due to itssurface layer without Me, thereby improving the photoluminescenceefficiency of the phosphor. However, the outer surface of the inorganiccoating layer coated phosphor has a limited thickness and insufficientwater resistance.

In the present invention, an inorganic coating layer A_(x)MF_(y) coatedsubstrate A_(x)MF_(y):Mn⁴⁺ is mixed with an organic solution containinga metal phosphate, an alkoxysilane, an organic carboxylic acid or anorganic amine. Then the organic solution is evaporated to give theorganic-inorganic coating layer coated substrate A_(x)MF_(y):Mn⁴⁺ (i.e.,the surface-modified fluoride luminescent material). Since thesurface-modified fluoride luminescent material has no excitation centerMn⁴⁺ at the interface between the inorganic coating layer and theorganic coating layer, the luminescence performance of the phosphor isless reduced.

Beneficial Effects:

(1) The surface-modified Mn⁴⁺-doped fluoride luminescent material of thepresent invention has a coating structure with an inorganic layer and anorganic layer that significantly improves the corrosion resistance ofthe fluoride phosphor. The modified phosphor has photoluminescenceintensity and quantum efficiency retention rate up to 85%-95% under hightemperature and high humidity conditions, and can be widely used in thefield of white LED backlight display.

(2) The inorganic coating layer in the present invention has the samecomposition as the phosphor substrate, and can be one or more layers.After the phosphor is coated with the inorganic coating layer, itssurface defects are reduced, and its photoluminescence intensity andquantum yield are increased by 5%-15%.

(3) The organic coating layer in the present invention avoids beingdirectly coated on the surface of the substrate A₂MF₆:Mn⁴⁺ phosphor,which prevents the direct contact between the organic coating layer andMn⁴⁺, thereby reducing the photoluminescence intensity and quantum yieldof the material. The organic layer can be one or more layers. After thephosphor is coated with the organic coating layer, its photoluminescenceintensity is reduced by only less than 3%. It can be seen that themodified material of the present invention not only improves thecorrosion and humidity resistance of the material, but also maintainsthe luminescence performance of the fluoride luminescent material.

(4) The surface modification method provided herein has the advantagesof low preparation temperature, short time, and easy process control,which is suitable for large-scale industrial preparation. In addition,the surface modification method provided herein has a wide range ofapplication, and therefore can be used for the surface modification ofsimilar phosphors with poor humidity resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the XRD diffraction pattern of the K₂TiF₆:Mn⁴⁺@K₂TiF₆@metalphosphate phosphor in (C) of Example 1 of the present invention.

FIG. 2 shows the XRD diffraction pattern of the K₂SiF₆:Mn⁴⁺@K₂SiF₆@metalphosphate phosphor in (C) of Example 2 of the present invention.

FIG. 3 shows the XRD diffraction pattern of the K₂GeF₆:Mn⁴⁺@K₂GeF₆@metalphosphate phosphor in (C) of Example 3 of the present invention.

FIG. 4 shows the scanning electron micrograph of the K₂TiF₆:Mn⁴⁺phosphor in (A) of Example 1 of the present invention.

FIG. 5 shows the scanning electron micrograph of the K₂TiF₆:Mn⁴⁺@K₂TiF₆phosphor in (B) of Example 1 of the present invention.

FIG. 6 shows the scanning electron micrograph of theK₂TiF₆:Mn⁴⁺@K₂TiF₆@metal phosphate phosphor in (C) of Example 1 of thepresent invention.

FIG. 7 shows the changes in photoluminescence intensity of the sampleencapsulated with the phosphors in Example 1 and Preparation Example 1of the present invention and with silica gel after aging at 85° C. and85% humidity.

FIG. 8 shows the changes in photoluminescence intensity of the sampleencapsulated with the phosphors in Example 2 and Preparation Example 2of the present invention and with silica gel after aging at 85° C. and85% humidity.

FIG. 9 shows the changes in photoluminescence intensity of the sampleencapsulated with the phosphors in Example 3 and Preparation Example 3of the present invention and with silica gel after aging at 85° C. and85% humidity.

FIG. 10 is a schematic diagram of the structure of the surface-modifiedphosphor according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION

The preparation method of the present invention will be furtherillustrated in detail with reference to the following specific examples.It should be understood that the following examples are merely exemplaryillustration and explanation of the present invention, and should not beconstrued as limiting the scope of protection of the present invention.All techniques implemented based on the aforementioned contents of thepresent invention are encompassed within the scope of protection of thepresent invention.

Unless otherwise stated, the experimental methods used in the followingexamples are conventional methods. Unless otherwise stated, thereagents, materials, and the like used in the following examples arecommercially available.

Instruments and Equipment

An X-ray powder diffractometer (DMAX 2500PC, Rigaku) was used for phaseanalysis; a field emission scanning electron microscopy (FE-SEM, HitachiSU1510) was used to observe the sample morphology; and an FLS980(Edinburgh Instrument) fluorescence spectrometer was used tocharacterize the fluorescence spectra of the samples.

The fluoride phosphor in the specific example of the present inventionhad a chemical general formula of A₂MF₆:Mn⁴⁺, wherein A was selectedfrom one of alkali metals Li, Na, K, Rb and Cs, and a combinationthereof; M was selected from one of Ti, Si, Ge, Sn, Zr, Al, Bi, Ga andIn, and a combination thereof; and Mn⁴⁺ was a luminescence center ion.The preparation process is as follows: an oxide, a salt or an acidcontaining M was dissolved in a 20%-50% HF solution according to theformula stoichiometric ratio of the Mn⁴⁺-doped fluoride phosphormaterial, and then the fluoride of A was added; after being stirred for1-10 min, the mixture was added with A₂MnF₆, stirred for 30-90 min, thenleft to stand, and filtered; and the resulting precipitate was washed,and dried to give the fluoride red phosphor A₂MF₆.

Preparation Examples 1-3: Preparation of A₂MF₆:Mn⁴⁺ Phosphor

The synthesis methods of Preparation Examples 1-3 were the same, exceptfor differences in the type and amount of starting materials. Thespecific parameters are shown in Table 1 below. The specific process wasillustrated by taking the K₂MF₆:Mn⁴⁺ phosphor of Preparation Example 1as an example: K₂MnF₆ was dissolved in a hydrofluoric acid solution;after being stirred for 1-10 min, the solution was added with the A₂MF₆powder, stirred at room temperature for 30-90 min, and filtered; and theresulting precipitate was washed with acetone to remove the residual HFcompletely, dried in an oven at 70° C. for 4 h to give the finalphosphor. The excitation and emission spectra, fluorescence quantumyield and absorption efficiency of the product were measured by anFLS980 (Edinburgh Instrument) fluorescence spectrometer. The results areshown in Table 2.

TABLE 1 Synthesis technical parameters of Preparation Examples 1-3 HFPreparation concen- Example Starting material Reaction time trationPreparation K₂TiF₆ 2.5 g K₂MnF₆ 0.18 g 30 min 49% Example 1 PreparationK₂SiF₆ 2.5 g K₂MnF₆ 0.10 g 90 min 49% Example 2 Preparation K₂GeF₆ 2.5 gK₂MnF₆ 0.12 g 60 min 49% Example 3

Example 1

(A) Preparation of Modified K₂TiF₆:Mn⁴⁺@K₂TiF₆ Phosphor

Compound K₂TiF₆ was added to a 49% HF solution (10 mL) until it was nolonger dissolved. The solution was filtered to remove the undissolvedK₂TiF₆ to give a saturated solution of K₂TiF₆ in the 49% HF solution.Then the saturated solution was added to a container containing theK₂TiF₆:Mn⁴⁺ phosphor (1 g) obtained in Preparation Example 1. Thesolution was stirred at room temperature for 30 min, filtered undervacuum, washed with acetone 3 times to remove the residual HF, and driedin an oven at 70° C. for 4 h to give the inorganic coating layer K₂TiF₆coated substrate K₂TiF₆:Mn⁴⁺, which was denoted as K₂TiF₆:Mn⁴⁺@K₂TiF₆phosphor. The excitation and emission spectra and internal fluorescencequantum yield of the product were measured by an FLS980 fluorescencespectrometer. The important luminescence performance parameters of theprepared phosphor are shown in Table 2.

(B) Preparation of Modified K₂TiF₆:Mn⁴⁺@Metal Phosphate Phosphor

P₂O₅ (0.0350 g) was added to an ethanol solution (10 mL). The solutionwas stirred continuously, and added with Al(NO₃)₃.9H₂O (0.1468 g) with amolar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. whilestirring, added with the K₂TiF₆:Mn⁴⁺ phosphor (1 g) in PreparationExample 1, heated and stirred until the solution was evaporated todryness. The residue was washed with acetone several times, dried in anoven at 140° C. for 4 h to give a phosphor, which was denoted asK₂TiF₆:Mn⁴⁺@metal phosphate phosphor. The important luminescenceperformance parameters of the prepared phosphor are shown in Table 2.

(C) Preparation of Modified K₂TiF₆:Me@K₂TiF₆@Metal Phosphate Phosphor

P₂O₅ (0.0350 g) was added to an ethanol solution (10 mL). The solutionwas stirred continuously, and added with Al(NO₃)₃.9H₂O (0.1468 g) with amolar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. whilestirring, added with the K₂TiF₆:Me@K₂TiF₆ phosphor (1 g) prepared in (A)of Example 1, heated and stirred until the solution was evaporated todryness. The residue was washed with acetone several times, dried in anoven at 140° C. for 4 h to give a phosphor, which was denoted asK₂TiF₆:Me@K₂TiF₆@metal phosphate phosphor. The X-ray powder diffractionshows that the product is still pure-phase K₂TiF₆ (FIG. 1), and no otherimpurity phases are introduced. The important luminescence performanceparameters of the prepared phosphor are shown in Table 2.

(D) Preparation of Modified K₂TiF₆:Me@K₂TiF₆@Octadecyl TrimethoxysilanePhosphor

Octadecyl trimethoxysilane (2.5 mL) was added to n-hexane (50 mL). Thesolution was stirred for 30 min, and added with the K₂TiF₆:Me@K₂TiF₆phosphor (1 g) prepared in (A) of Example 1. Then the solution washeated to 70° C. and stirred until the solution was evaporated todryness. The residue was washed with n-hexane several times, dried in anoven at 150° C. for 4 h to give a phosphor, which was denoted asK₂TiF₆:Me@K₂TiF₆@octadecyl trimethoxysilane phosphor. The importantluminescence performance parameters of the prepared phosphor are shownin Table 2.

FIGS. 4-6 are the scanning electron micrographs of the phosphorsprepared in (A), (B) and (C) of Example 1. It can be seen from thosefigures that the inorganic coating layer coated sample has a smoothsurface and an unchanged particle size, and the organic coating layercoated sample has a small amount of fine substances on the surface.

Example 2

(A) Preparation of Modified K₂SiF₆:Me@K₂SiF₆ Phosphor

Compound K₂SiF₆ was added to a 49% HF solution (10 mL) until it was nolonger dissolved. The solution was filtered to remove the undissolvedK₂SiF₆ to give a saturated solution of K₂SiF₆ in the 49% HF solution.Then the saturated solution was added to a container containing theK₂SiF₆:Mn⁴⁺ phosphor (1 g) obtained in Preparation Example 2. Thesolution was stirred at room temperature for 30 min with an ethanolbeing added dropwise at 0.5 mL/min. Then the solution was filtered undervacuum, washed with acetone 3 times to remove the residual HF, and driedin an oven at 70° C. for 4 h to give the K₂SiF₆:Me@K₂SiF₆ phosphor. Theexcitation and emission spectra and internal fluorescence quantum yieldof the product were measured by an FLS980 fluorescence spectrometer. Theimportant luminescence performance parameters of the prepared phosphorare shown in Table 2.

(B) Preparation of Modified K₂SiF₆:Me@Metal Phosphate Phosphor

P₂O₅ (0.0350 g) was added to an ethanol solution (10 mL). The solutionwas stirred continuously, and added with Al(NO₃)₃.9H₂O (0.1468 g) with amolar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. whilestirring, added with the K₂SiF₆:Mn⁴⁺ phosphor (1 g) in PreparationExample 2, heated and stirred until the solution was evaporated todryness. The residue was washed with acetone several times, dried in anoven at 140° C. for 4 h to give a phosphor. The important luminescenceperformance parameters of the prepared phosphor are shown in Table 2.

(C) Preparation of Modified K₂SiF₆:Me@K₂SiF₆@Metal Phosphate Phosphor

P₂O₅ (0.0350 g) was added to an ethanol solution (10 mL). The solutionwas stirred continuously, and added with Al(NO₃)₃.9H₂O (0.1468 g) with amolar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. whilestirring, added with the K₂SiF₆:Me@K₂SiF₆ phosphor (1 g) prepared in (A)of Example 2, heated and stirred until the solution was evaporated todryness. The residue was washed with acetone several times, dried in anoven at 140° C. for 4 h to give a phosphor. The X-ray powder diffractionshows that the product is still pure-phase K₂SiF₆ (FIG. 2), and no otherimpurity phases are introduced. The important luminescence performanceparameters of the prepared phosphor are shown in Table 2.

(D) Preparation of Modified K₂SiF₆:Me@K₂SiF₆@Hexadecyl TrimethoxysilanePhosphor

Hexadecyl trimethoxysilane (5 mL) was added to n-hexane (50 mL). Thesolution was stirred for 30 min, and added with the K₂SiF₆:Me@K₂SiF₆phosphor (1 g) prepared in (A) of Example 2. Then the solution washeated to 70° C. and stirred until the solution was evaporated todryness. The residue was washed with n-hexane several times, dried in anoven at 150° C. for 4 h to give a phosphor, which was denoted asK₂SiF₆:Me@K₂SiF₆@hexadecyl trimethoxysilane phosphor. The importantluminescence performance parameters of the prepared phosphor are shownin Table 2.

Example 3

(A) Preparation of Modified K₂GeF₆:Me@K₂GeF₆ Phosphor

Compound K₂GeF₆ was added to a 49% HF solution (10 mL) until it was nolonger dissolved. The solution was filtered to remove the undissolvedK₂GeF₆ to give a saturated solution of K₂GeF₆ in the 49% HF solution.Then the saturated solution was added to a container containing theK₂GeF₆:Mn⁴⁺ phosphor obtained in Preparation Example 3. The solution wasstirred at room temperature for 30 min with an ethanol being addeddropwise at 0.5 mL/min. Then the solution was filtered under vacuum,washed with acetone 3 times to remove the residual HF, and dried in anoven at 70° C. for 4 h to give the K₂GeF₆:Me@K₂GeF₆ phosphor. Theexcitation and emission spectra and internal fluorescence quantum yieldof the product were measured by an FLS980 fluorescence spectrometer. Theimportant luminescence performance parameters of the prepared phosphorare shown in Table 2.

(B) Preparation of Modified K₂GeF₆:Me@Metal Phosphate Phosphor

P₂O₅ (0.0350 g) was added to an ethanol solution (10 mL). The solutionwas stirred continuously, and added with Al(NO₃)₃.9H₂O (0.1468 g) with amolar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. whilestirring, added with the K₂GeF₆:Mn⁴⁺ phosphor (1 g) in PreparationExample 3, heated and stirred until the solution was evaporated todryness. The residue was washed with acetone several times, dried in anoven at 140° C. for 4 h to give a phosphor. The important luminescenceperformance parameters of the prepared phosphor are shown in Table 2.

(C) Preparation of Modified K₂GeF₆:Me@K₂GeF₆@Metal Phosphate Phosphor

P₂O₅ (0.0350 g) was added to an ethanol solution (10 mL). The solutionwas stirred continuously, and added with Al(NO₃)₃.9H₂O (0.1468 g) with amolar ratio of 1:1 of Al:P. Then the solution was heated to 70° C. whilestirring, added with the K₂GeF₆:Mn⁴⁺@K₂GeF₆ phosphor (1 g) prepared in(A) of Example 3, heated and stirred until the solution was evaporatedto dryness. The residue was washed with acetone several times, dried inan oven at 140° C. for 4 h to give a phosphor. The X-ray powderdiffraction shows that the product is still pure-phase K₂GeF₆ (FIG. 3),and no other impurity phases are introduced. The important luminescenceperformance parameters of the prepared phosphor are shown in Table 2.

(D) Preparation of Modified K₂GeF₆:Mn⁴⁺@K₂GeF₆@Dodecyl TrimethoxysilanePhosphor

Dodecyl trimethoxysilane (5 mL) was added to n-hexane (50 mL). Thesolution was stirred for 30 min, and added with the K₂GeF₆:Mn⁴⁺@K₂GeF₆phosphor (1 g) prepared in (A) of Example 3. Then the solution washeated to 70° C. and stirred until the solution was evaporated todryness. The residue was washed with n-hexane several times, dried in anoven at 150° C. for 4 h to give a phosphor, which was denoted asK₂GeF₆:Mn⁴⁺@K₂GeF₆@dodecyl trimethoxysilane phosphor. The importantluminescence performance parameters of the prepared phosphor are shownin Table 2.

TABLE 2 Luminescence performance parameters of aged samples QuantumRelative System Example yield AbsorptanceAbsorptance luminanceK₂TiF₆:Mn⁴⁺ Preparation 93% 71% 94% Example 1 Example 1 (A) 98% 68%100%  Example 1 (B) 85% 60% 88% Example 1 (C) 94% 67% 95% Example 1 (D)93% 65% 94% K₂SiF₆:Mn⁴⁺ Preparation 91% 64% 91% Example 2 Example 2 (A)96% 62% 100%  Example 2 (B) 84% 56% 85% Example 2 (C) 93% 61% 93%Example 2 (D) 92% 60% 92% K₂GeF₆:Mn⁴⁺ Preparation 89% 58% 92% Example 3Example 3 (A) 94% 56% 100%  Example 3 (B) 81% 52% 86% Example 3 (C) 91%55% 94% Example 3 (D) 90% 54% 91%

It can be seen from Table 2 that an inorganic coating layer coatedphosphor has increased quantum yield and luminance but a slightlydecreased absorptance; an organic coating layer coated phosphor hassignificantly decreased luminance and quantum yield; and aninorganic-organic coating layer coated phosphor has a basicallyunchanged or slightly increased quantum yield as compared to an uncoatedphosphor.

Example 4. Stability Test

Each of the phosphor samples (0.1 g) prepared in Preparation Examples1-3 and Examples 1-3 was mixed well with silica gel (A and B),encapsulated in a customized polytetrafluoroethylene mold, defoamed andhardened to give phosphor films. The films were aged in a programmabletemperature & humidity chamber at 85° C. and 85% relative humidity. Thespectrum and quantum efficiency of the samples were measured every 24 hto evaluate the high temperature and high humidity stability of thephosphors.

FIGS. 7, 8 and 9 show the changes in photoluminescence intensity of theabove phosphors after aging at 85° C. and 85% relative humidity. It canbe seen from FIG. 7 that the humidity resistance of theinorganic-organic coating layer coated phosphor disclosed herein hasbeen greatly improved. After 240 h, the photoluminescence intensity ofthe phosphor prepared in (C) of Example 1 still maintains 92%. Thephotoluminescence intensity of the inorganic coating layer coatedfluoride phosphor ((A) of Example 1) is only 83%, and thephotoluminescence intensity of the fluoride phosphor without surfacemodification (prepared in Preparation Example 1) is only 59%. It can beseen that the inorganic-organic layer coating achieves a more excellenteffect compared with the organic layer coating or the inorganic layercoating. The aging test results of other examples and preparationexamples are similar (see FIG. 8 and FIG. 9).

The examples of the present invention have been described above.However, the present invention is not limited to the above examples. Anymodification, equivalent, improvement and the like made withoutdeparting from the spirit and principle of the present invention shallfall within the protection scope of the present invention.

1. A surface-modified fluoride luminescent material, wherein theluminescent material comprises a substrate, an inorganic coating layerand an organic coating layer, the inorganic coating layer being coatedon the outer surface of the substrate, and the organic coating layerbeing coated on the outer surface of the inorganic coating layer;wherein the substrate is A_(x)MF_(y):Mn⁴⁺, and the inorganic coatinglayer is A_(x)MF_(y); wherein A is selected from one of alkali metalsLi, Na, K, Rb and Cs and a combination thereof; M is selected from oneof Ti, Si, Ge, Sn, Zr, Al, Bi, Ga and In, and a combination thereof; xis an absolute value of the charge of [MF_(y)] ion; y is 4, 5, 6 or 7;and Mn⁴⁺ is a luminescence center ion.
 2. The surface-modified fluorideluminescent material according to claim 1, wherein x is an absolutevalue of the charge of [MF₆] ion, and y is
 6. 3. The surface-modifiedfluoride luminescent material according to claim 1, wherein theinorganic coating layer can be a single layer or multiple layers, andthe organic coating layer coated on the outer surface of the inorganiccoating layer can also be a single layer or multiple layers.
 4. Thesurface-modified fluoride luminescent material according to claim 1,wherein the organic coating layer is at least one of metal phosphate,alkoxysilane, organic carboxylic acid and organic amine.
 5. Thesurface-modified fluoride luminescent material according to claim 1,wherein the phosphate in the metal phosphate is phosphomonoester orphosphodiester, such as P(O)(OH)₂(OR) or P(O)(OH)(OR)₂, wherein R ishydrocarbyl; preferably, the phosphate is obtained by esterifying aphosphorus source with an alcohol, wherein the phosphorus source isselected from one of P₂O₅ and POCl₃, or a combination thereof; and thealcohol is at least one selected from methanol, ethanol, n-propanol,isopropanol, n-butanol and isobutanol; preferably, the metal in themetal phosphate is selected from one of Al, Ti, Si, Ga and Zn ions, anda combination thereof; preferably, the alkoxysilane is Si(OR¹)₃(R²),wherein R¹ is C₁₋₆ alkyl, and R² is C₁₋₂₀ alkyl or C₁₋₂₀ alkenyl; forexample, the alkoxysilane is selected from methyl trimethoxysilane,ethyl trimethoxysilane, n-propyl trimethoxysilane, n-octyltrimethoxysilane, ethenyl trimethoxysilane, dodecyl trimethoxysilane,hexadecyl trimethoxysilane, and octadecyl trimethoxysilane; preferably,the organic carboxylic acid is R³COOH, wherein R³ is C₁₋₃₀ alkyl; forexample, the organic carboxylic acid is selected from oleic acid,stearic acid, docosanoic acid, octacosanoic acid, and lauric acid;preferably, the organic amine is NR⁴(R⁵)₂, wherein R⁴ is C₁₋₁₀ alkyl,and R⁵, which may be the same or different, is H or C₁₋₁₀ alkyl; forexample, the organic amine is selected from methylamine, ethylamine,propylamine, butylamine, octylamine, and hexylamine, and thecorresponding secondary amine or tertiary amine.
 6. A preparation methodfor the surface-modified fluoride luminescent material according toclaim 1, comprising the following steps: (1) dissolving the compoundA_(x)MF_(y) in hydrofluoric acid solution to form a saturated solution;(2) adding the substrate A_(x)MF_(y):Mn⁴⁺ into the saturated solution instep (1), and obtaining an substrate A_(x)MF_(y):Mn⁴⁺ coated withinorganic coating layer A_(x)MF_(y) by ion exchange reaction, which isdenoted as A_(x)MF_(y):Mn⁴⁺@A_(x)MF_(y); (3) preparing an organicsolution; (4) mixing the substrate A_(x)MF_(y):Mn⁴⁺ coated withinorganic coating layer A_(x)MF_(y) obtained in step (2) with theorganic solution in step (3), and heating and stirring the mixture untilthe organic solvent is removed, to give the surface-modified fluorideluminescent material, which is denoted as A_(x)MF_(y):Mn⁴⁺@A_(x)MF_(y)organic layer; wherein A is selected from one of alkali metals Li, Na,K, Rb and Cs, or a combination thereof; M is selected from one of Ti,Si, Ge, Sn, Zr, Al, Bi, Ga and In, or a combination thereof; x is anabsolute value of the charge of [MF_(y)] ion; y is 4, 5, 6 or 7; andMn⁴⁺ is a luminescence center ion.
 7. The preparation method accordingto claim 6, wherein in step (2), the mass ratio of the substrateA_(x)MF_(y):Mn⁴⁺ to the compound A_(x)MF_(y) in the saturated solutionin step (1) is 10:1-1:5, and preferably, 1:1; preferably, in step (2),the ion exchange process is performed at 0-100° C., and preferably, at25-80° C.
 8. The preparation method according to claim 6, wherein instep (3), the organic solution is at least one of a metal phosphatesolution, an alkoxysilane solution, an organic carboxylic acid solutionand an organic amine solution, and the preparation process for thesolution is, for example: dissolving an alkoxysilane, an organiccarboxylic acid or an organic amine in an organic solvent, wherein theorganic solvent is at least one selected from methanol, ethanol,propanol, n-hexane, and cyclohexane; mixing a metal source and aphosphorus source with an alcohol for esterification to give a metalphosphate solution, wherein the phosphorus source is selected from oneof P₂O₅ and POCl₃, or a combination thereof; the alcohol is at least oneselected from methanol, ethanol, n-propanol, isopropanol, n-butanol, andisobutanol; and the metal source is metal nitrate, metal sulfate ormetal oxalate, or one or more of metal organic salts such asisopropoxide, ethoxide, propoxide or butoxide, and preferably, the metalsource is Al(NO₃)₃.9H₂O, Zn(NO₃)₂.6H₂O, titanium butoxide, or aluminumisopropoxide.
 9. The preparation method according to claim 6, wherein instep (4), the temperature of the heating and stirring is at least 30°C., and preferably, at least 50° C.; preferably, in step (4), the massratio of the substrate A_(x)MF_(y):Mn⁴⁺ coated with inorganic coatinglayer A_(x)MF_(y) to the organic solution is 5:1-1:20, and preferably,1:1-1:5.
 10. The method according to claim 6, wherein in step (2), theA_(x)MF_(y):Mn⁴⁺ is selected from A₂MF₆:Mn⁴⁺ and A₃MF₆:Mn⁴⁺, wherein theA₂MF₆:Mn⁴⁺ is selected from K₂TiF₆:Mn⁴⁺, K₂SiF₆:Mn⁴⁺, Na₂SiF₆:Mn⁴⁺,Na₂TiF₆:Mn⁴⁺, K₂GeF₆:Mn⁴⁺, Na₂SnF₆:Mn⁴⁺, Cs₂TiF₆:Mn⁴⁺ and Cs₂SiF₆:Mn⁴⁺;and the A₃MF₆:Mn⁴⁺ is selected from Na₃AlF₆:Me, K₃AlF₆:Mn⁴⁺,Li₃AlF₆:Mn⁴⁺, Rb₃AlF₆:Mn⁴⁺, Cs₃AlF₆:Mn⁴⁺, K₂NaAlF₆:Mn⁴⁺ andK₂LiAlF₆:Mn⁴⁺; and preferably, in step (1), the A_(x)MF_(y) is selectedfrom A₂MF 6 and A₃MF₆, wherein the A₂MF₆ is selected from K₂TiF₆,K₂SiF₆, Na₂SiF₆, Na₂TiF₆, K₂GeF₆, Na₂SnF₆, Cs₂TiF₆ and Cs₂SiF₆; and theA₃MF₆ is selected from Na₃AlF₆, K₃AlF₆, Li₃AlF₆, Rb₃AlF₆, Cs₃AlF₆,K₂NaAlF₆ and K₂LiAlF₆.